86 Ghiberto et al.

Nitrogen in an cultivated with

Pablo Javier Ghiberto1,3; Paulo Leonel Libardi2,3*; Alexsandro dos Santos Brito3; Paulo Cezar Ocheuze Trivelin3,4

1 UNL/FCA – Depto. de Ciencias del Ambiente, Kreder 2805, PO Box S3080HOF – Esperanza, SF – Argentina. 2 USP/ESALQ – Depto. de Engenharia de Biossistemas, C.P. 09 – 13418-900 – Piracicaba, SP – Brasil. 3 USP/ESALQ – Programa de Pós-Graduação em Solos e Nutrição de Plantas. 4 USP/CENA – Laboratório de Isótopos Estáveis, C.P. 96 – 13416-000 – Piracicaba, SP – Brasil. *Corresponding author

ABSTRACT: Nitrogen (N) leaching below the crop-rooting zone represents not only a valuable loss of nutrients for the plant, but also a potential pollution source of groundwater. The objective of this work was to quantify leaching losses of native N and that derived from fertilizer in an Oxisol that was cultivated with sugarcane (Saccharum officinarum) during the crop plant cycle. The sugarcane was planted and fertilized with urea in the planting furrow, with 120 kg ha–1 of N. In order to determine the fate of the fertilizer - N, four microplots with 15N enriched fertilizer were installed. Input and output of N at the depth of 0.9 m were quantified from the flux density of water and the N concentration in solution. During the evaluation period the rainfall was 141 mm less than the historical average (1,315 mm), and the was drier than normal in January. The average concentration of N in soil solution was 1.8 mg L–1. The abundance of 15N was very high at the beginning (first week) of the assessment period and remained approximately constant (0.453 atom% of 15N) until the end of the period. The internal drainage was 91 mm of water and the N leaching loss was 1.1 kg ha–1 of N, with only 54 g ha–1 derived from fertilizer. Therefore, under high demand of N by the crop in a system without burning before planting, the leaching of N was not considerable, mainly because the surplus of water between the months of December and March was lower than expected and also because the extraction of nitrogen by the crop was high. Key words: Saccharum spp., sustainability, solute transport, environmental quality, pollution

Nitrogênio lixiviado num Latossolo cultivado com cana-de-açúcar

RESUMO: A lixiviação de nitrogênio (N) abaixo da zona radicular representa uma valiosa perda do nutriente para as plantas e uma fonte potencial de poluição do lençol freático. Quantificaram-se as perdas de N por lixiviação num Latossolo Vermelho Amarelo cultivado com cana-de-açúcar (Saccharum officinarum) durante o ciclo agrícola de cana-planta. A cultura foi implantada e fertilizada no sulco com 120 kg ha–1 de N-uréia. Para conhecer o destino do fertilizante, foram instaladas quatro microparcelas onde o fertilizante era marcado com o isótopo 15N. As entradas e saídas de N a 0,9 m de profundidade foram quantificadas diariamente pela densidade de fluxo de água e a concentração de N da solução no solo. No período de avaliação, a precipitação pluvial foi 141 mm menor que a média histórica (1.315 mm) sendo janeiro mais seco que o normal. A concentração de N mineral média foi 1,8 mg L–1. A abundância de 15N foi superior à abundância natural do isótopo, especialmente no início do período de avaliação, permanecendo logo constante (0,453% de 15N). A drenagem interna foi de 91 mm de água e a perda por lixiviação foi 1,1 kg ha–1 de N com apenas 54 g ha–1 derivados do fertilizante. Portanto, com elevada demanda de nutrientes e elevada incorporação de restos culturais, não foram registradas perdas apreciáveis de N por lixiviação devido ao fato de o excedente de água entre os meses de dezembro e março ter sido menor que o esperado e pela elevada extração de N pela cana-de-açúcar. Palavras-chave: Saccharum spp., sustentabilidade, transporte de solutos, qualidade ambiental, poluição

Introduction of management systems that avoid negative impacts on soil, water and biodiversity (Goldemberg et al., 2008; Since the initiation of the Proalcohol program in Hartemink, 2008; Martinelli and Filoso, 2008). in 1975, sugarcane (Saccharum officinarum) for Under this context, fertilization with nitrogen (N) producing ethanol for fuel has increased in cultivated should be carefully assessed for sustainability because area and productivity, mainly in the São Paulo State. The high N use efficiency is directly related to lower risk of expansion of ethanol production from sugarcane gener- groundwater and air pollution, smaller losses of nutri- ates discussions about social and environmental issues ents by leaching and lower risk of , be- (Goldemberg et al., 2008; Hartemink, 2008; Uriarte et al., sides the direct benefits of increased sugarcane produc- 2009), with emphasis in the agricultural sector on the use tivity and decreased production costs. One of the main

Sci. Agric. (Piracicaba, Braz.), v.68, n.1, p.86-93, January/February 2011 Nitrogen fertilizer leaching in an Oxisol 87 problems with nitrogen fertilization in sugarcane is the Material and Methods low N recovery by the crop (Hartemink, 2008), between 10 to 40% as measured in the field using 15N tracer iso- The experiment was carried out near Pirassununga, tope (Chapman et al., 1994; Trivelin et al., 1995; Vallis et state of São Paulo, Brazil (21º55’ S, 47º10’ W, 650 m a.s.l.). al., 1996). Thus, the portion of N not used by the crop The climate, according to the Köeppen classification, is may remain in the soil, be incorporated as organic mat- of the Aw type: tropical of savanna. Based on 30 years ter, be lost to the atmosphere or leach below the root zone of meteorological data from the location, the annual av- where crops effectively extract water and nutrients. erage temperature is 21.7ºC and the annual average rain- In São Paulo State, there are few studies on N leach- fall is 1,343 mm, with higher frequency between Decem- ing by means of direct monitoring in the field, espe- ber and March (840 mm) (Sentelhas et al., 2008). By us- cially with doses higher than normally used during the ing the climatological water balance method of sugarcane crop plant cycle (30 to 90 kg ha–1 of N, Thornthwaite and Mather (1955), rainfall exceeds poten- Cantarella et al., 2007). We hypothesize that doses of tial evapotranspiration between December and March, N higher than those normally used will originate leach- producing a water excess of 381 mm. The soil is a Typic ing of N. Considering that this is important to find ex- Eutrustox (Table 1 and 2) of sandy texture, planatory variables for predicting or explaining N with a water table over the depth of 10 m. The method- leaching, and to generate information that allows the ology used in this study was similar to that presented planning of sustainable crop management practices, the by Ghiberto et al. (2009). objective of this study was to quantify the leaching loss Before sugarcane planting, 2 t ha–1 of dolomite lime- of native nitrogen and that derived from fertilizer in stone was applied over the entire experimental area. an Oxisol of the State of São Paulo (Brazil) cultivated Then, the sugarcane (variety SP81-3250) was planted and with sugarcane during the agricultural cycle of the crop fertilized with urea (120 kg ha–1 of N) in the planting fur- plant. row between February 21 and 24, 2005. In addition, 120

Table 1 – Chemical attributes of the soil.

Soil pH Depth PKaCgMlAlHC+ A CE Horizon ∆ H2OlKC pH –1 –1 mgmg k ------mmolc kg ------

Ap 0.20 7.2 6.2 -1 10 1.9 43 11 0 8 63.9 B4A 05.4 61. 64. -160. 27301. 1623.

Bw1 0.81 6.9 6.2 -0.7 2 2.5 11 4 0 10 27.5 + Bw2 0.81 61.4 63. -180. 18. 17011837. pH : pH in water, ratio 1:2.5; pH : pH in 1 M KCl ratio 1:2.5; ΔpH= pH -pH ; P: extraction by ionic exchanger resin and H2O KCl KCl H2O determination by colorimetry; K and Na: extraction by Mehlich1 solution and determination by flame photometry; Ca, Mg: extraction by ion exchanger resin and determination by spectrometry of atomic absorption; H+Al: determination by 0.5 M calcium acetate pH=7; Cation exchange capacity: CEC = Na + K + Ca + Mg + Al.

Table 2 – Particle size distribution, bulk density (ρb), particle density (ρp) and total porosity (TP) of the soil. Particle size distribution Depth ρ ρ TP Stand Syil Cla b p mg------g k –1 -m------kg –3 -%------0.1 733 52 215 1609 2681 40.0 00.2 702 60282 1368 2767 36. 0.3 705 55 240 1681 2682 37.3 08.4 677 75224 1553 2068 43. 0.5 695 50 255 1528 2693 43.3 08.6 635 70217 1445 2169 46. 0.7 673 48 280 1407 2692 55.6 05.8 603 85228 1439 2369 48. 0.9 675 40 285 1427 2695 47.1 15.0 683 78288 1529 2869 51.

Particle size distribution: pipette method; ρb: undisturbed soil samples in 0.05 × 0.05 m cores; ρp: helium pycnometer; TP= (1-ρb /ρp).

Sci. Agric. (Piracicaba, Braz.), v.68, n.1, p.86-93, January/February 2011 88 Ghiberto et al.

–1 kg ha of K2O and P2O5 with the sources potassium chlo- 0.9 m was calculated by finite difference from daily read- ride (KCl) and triple superphosphate, respectively, were ings of tensiometers at the depths of 0.8 m and 1.0 m. The also applied. To determine the fate of the N-fertilizer, K(θ) function was determined by the instantaneous pro- four microplots were installed. They consisted of 2.0 m file method (Hillel et al., 1972) by means of equation (3): of planting line, i.e., 2.0 m × 1.5 m since the spacing be- K(θ) = K expγ (θ – θ ) (3) tween the rows is 1.5 m (Trivelin et al., 1994), in which 0 0 15 nitrogen fertilizer enriched to 5.04 N At% was applied. –1 in which Ko = 443.3 mm d (at time zero of Input and output of N ions, at the 0.9 m depth, were 3 –3 redistribution); γ = 52.232 and θo = 0.366 m m (at time evaluated from the flux densities of water and the ion zero of soil water redistribution). concentrations; tensiometers, the soil water retention Soil bulk density (rb) was determined at depths of 0.1, curve and soil solution extractors with porous cups were 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 m using an Uhland used for this purpose. The equipment was installed in sampler. Three soil cores (diameter of 0.05 m and height the field at the end of August 2005, just after leveling of of 0.05 m) were taken per depth. The soil water reten- the soil between plant rows. Because it was not possible tion curve at the 0.9 m depth was determined for the to install the equipments before leveling the soil between matric potentials -0.5, -1, -3, -5, -7 and -10 kPa by using plant rows, there was the delay between fertilization and porous plate funnels and, for -30, -50, 70 and -100 kPa, in beginning of the measurements. For this it was assumed Richard’s pressure cells. Three soil cores were saturated that the release of N was low because of the high incor- and equilibrated at each potential, and then the gravi- poration of crop residues with a C/N of around 100, metric and volumetric soil water content was calculated which facilitates the immobilization process (Oliveira using the soil bulk density. Finally, the data were ad- et al., 1999). On other hand, near the town of justed to equation (4) (van Genuchten, 1980): Pirassununga, in the period without measurements, the n –m climatological water balance is negative, which means θ = θr + (θs – θr) [1 + (a| ψm|) ] (4) that there is no surplus water to drain and transport sol- where θ = 0.455 m3 m–3 is the saturated soil water con- utes below the root-zone. s tent; θ = 0.126 m3 m–3 is the soil residual water content; One tensiometer was installed at each of the depths r α = 0.542 kPa, n = 5.0463 and m = 0.1668 are adjust- of 0.8, 0.9 and 1.0 m, and a solution extractor was in- ment parameters; and y is the matric potential. stalled at the depth of 0.9 m in each microplot. The 0.9 m The solution taken from the soil was filtered m depth was adopted because in this region, most sug- (millipore cellulose filter paper 0.45 μm) and the con- arcane root biomass is found close to the soil surface; + – – centration of the ions NH4 , NO3 and NO2 determined in fact, 80% occurs within the top 0.6 m (Ball-Coelho et by ion chromatography (DIONEX ICS-90). The 15N al., 1992; Smith et al., 2005). Ion movement was measured analyses to quantify the N in the soil solution derived by integrating the daily ion flux density over the time from fertilizer were made by means of a mass spectrom- period, as indicated in equation (1) for NO –: 3 eter (ANCA-GSL by Secon). However, composite t f samples from each extractor were used in sequence to

q − = q w C − dt (1) NO3 ∫ NO3 obtain reliable measurements on the mass spectrometer t0 –1 when the total mineral N content in the sample was less where q − (kg ha ) is the flow of nitrate in the soil, q NO3 w than 150 to 250 mg N. Thereafter, each sample was con- –1 is the soil water flux density (m d ), and C − is the NO3 centrated by distillation in alkaline medium with –1 concentration of nitrate in the soil solution (kg L ) at Devarda alloy (Cantarella and Trivelin, 2001). The per- the moment of measurement. t0 and tf represent the ini- centage of nitrogen in the soil solution derived from the tial time (equipment installation) and final time (harvest) fertilizer (%NSSDF) was calculated by equation (5), of the experiment. The same procedure was carried out adapted from Hauck et al. (1994): – + to estimate the flow of NO2 and NH4 . The soil water flux density at the depth of 0.9 m was %NSSDF = [(Atom%solution – Atom%soil)/(Atom%fertilizer – Atom%soil)] × 100 estimated from August/2005 (installation of equipment) (5) until June/2006 (sugarcane harvest) using the Darcy- 15 where Atom% is the N abundance of the fertilizer Buckingham equation (equation 2): (5.04%) and of the soil (0.367%). θ = – K(θ)Δ(ψ )/L (2) The soil water storage (H) was determined by the w t gravimetric method in each replicate by sampling of the –1 where K(θ) is the soil hydraulic conductivity (m d ) as following soil layers: 0 - 0.15, 0.15 - 0.25, 0.25 - 0.35, 0.35 - a function of the volumetric water content (θ), or K(θ) 0.45, 0.45 - 0.55, 0.55 - 0.65, 0.65 - 0.75, 0.75 - 0.85, 0.85 - function, and Δψt/L is the soil water total potential gra- 0.95 and 0.95 - 1.05 m, approximately every 20 d. Each dient, both at the depth of 0.9 m. sample was placed in an aluminum can, hermetically The volumetric soil water content, used to estimate K sealed, and transported to the laboratory, where the during the experiment, was obtained from daily readings gravimetric and volumetric soil water contents were de- of the tensiometers and the soil water retention curve at termined using the soil bulk density of each depth and the depth of 0.9 m. The gradient (Dyt/L) at the depth of then calculating the soil water storage (Gardner, 1986).

Sci. Agric. (Piracicaba, Braz.), v.68, n.1, p.86-93, January/February 2011 Nitrogen fertilizer leaching in an Oxisol 89

Daily rainfalls were measured by means of a ary, Table 3 and Figure 1). Then, with atypical rainfalls pluviometer installed at the experiment site and com- in late February, the storage of water was elevated in pared to the historical series of Pirassununga between the period of February 21, 2006 to April 12, 2006. 1939 and 2004, obtained from the pluviometric database The evolution of the volumetric soil water content of the State of São Paulo. at 0.9 m depth was similar to the storage of water in the soil profile during the monitoring period (Figure 1). The Results and Discussion volumetric water content (θ), inferred from the tensiom- eter readings, was less than 0.15 m3 m–3 from the begin- Rainfall between September 1, 2005 and May 31, 2006 ning of the experiment to December 24, 2005. After that, amounted to 1,174 mm, which is 141 mm less than the there was an increase in θ, with the maximum value of historical average over the same period (1,315 mm) 0.278 m3 m–3 at January 5, 2006. According to the results, (Table 3). Even though January is the rainiest month of 3 –3 θ never reached saturation (θs = 0.455 m m , adjustment the year, rainfall was recorded to be 71 mm less than parameter of equation 4) or θo (parameter of the K(θ) normal. On the other hand, February exceeded the av- function of equation 3), but exceeded in three circum- erage by 103 mm. According to Tollner (2002), the re- stances the field capacity at the depth of 0.9 m. turn period of an equal or greater event for February is It was possible to extract the soil solution only in seven years. The rainfall distribution was similar to the the period between December 26, 2005 and April 28, historical average in the remaining months of monitor- 2006, when the soil water matric potential was higher ing. than -40 kPa. The mean mineral N concentration dur- From December 5, 2005 to December 22, 2005, the ing the experiment was 1.8 mg L–1 with a standard devia- soil water storage down to a depth of 0.9 m increased tion of 2.2. At the beginning of the extraction period, the by 48 mm following an increase in the rainfall of 116 N concentration was higher than in the later period (Fig- mm (Figure 1). After this period, the soil profile had a ure 2). The At% of 15N was higher than the natural abun- volumetric soil water content around the field capacity dance of the isotope (0.367 At% of 15N) from the begin- 3 –3 (FC) until January 10, 2006 (FC= 0.237 m m for ψm= ning of the evaluation period, decreasing subsequently -10 kPa). Next, during the phenological phase of maxi- and remaining almost constant (0.453 At% of 15N) from mum growth of sugarcane (Franco 2008), with high wa- December 28, 2005 to February 15, 2006 (Figure 2). ter demand by the crop and coinciding with a period of Coinciding with the rain periods 3, 5 and 7, the volu- low precipitation, the soil water storage decreased (Janu- metric soil water content exceeded field capacity and

Table 3 – Monthly average rainfall in Pirassununga in the period 1939-2004 and during the months of the experiment. Monthly rainfall distribution (mm) Year S.ep. O.ct N.ov D.ec J.an F.eb M.ar Aypr Ma 2005/2006 61 121 153 230 244 217 166 69 54 665 yr average 597653233 107 322 230 53

Table 4 – Rainfall, drained water and nitrogen flow in the soil at various periods; positive numbers indicate gains and negative numbers indicate losses of water and nitrogen at the depth of 0.9 m. Period N leaching† Reainfall Drainag 15 Ne° DLat NO-TOTA N-N 2-ON-N 3-HN-N 4+ N-Fert. mam ------kg h –1 ------1 08/24 - 11/30 191 0.1 (0.7) 0.0 (0.0) 0.000 0.014 0.001 0.004 24112/01 - 12/1 6)-)0.1 (0.0 00.0 (0.0 06.00 -10.00 -20.00 -0.00 3 12/15 - 01/08 326 -22.3 (11.4) -0.4 (0.4) -0.010 -0.226 -0.155 -0.043 41091/09 - 01/3 1)-)0.9 (1.1 00.0 (0.0 01.00 -60.00 -00.00 0.00 5 02/01 - 02/20 297 -49.4 (32.4) -0.6 (0.3) -0.087 -0.162 -0.354 -0.010 68022/21 - 03/1 9)-)4.1 (1.1 05.0 (0.0 -70.00 -50.00 -10.03 -0.00 7 03/19 - 03/29 131 -9.6 (12.2) -0.1 (0.0) -0.011 -0.023 -0.028 -0.001 81083/30 - 05/3 5)-)4.7 (2.0 00.0 (0.0 -10.01 -70.01 -10.02 -0.00 Total 1175 -91.0 (60.9) -1.1 (0.7) -0.123 -0.422 -0.605 -0.054 The numbers shown for each period represent the average of four repetitions, and the respective standard deviations. The number shown as the total of the cycle is the sum of each period and the respective standard deviation propagated. (†) In the experiment: 120 –1 –1 –1 kg ha of N; 120 kg ha of K2O and P2O5; and 2 t ha of dolomite limestone were applied.

Sci. Agric. (Piracicaba, Braz.), v.68, n.1, p.86-93, January/February 2011 90 Ghiberto et al.

80 Soil Water Storage Volumetric Water Content 0.30 70 )

250 –1 0.25 60 200

) 50

0.20 –3

m 40

150 3 0.15

H (mm) 30 100 q (m 0.10 20

50 0.05 10 Water flow or Rainfall (mm d (mm Rainfall or flow Water 0 0.00 0 10/3 11/12 12/22 1/31 3/12 4/21 5/31 -10 Date -20 Date Figure 1 – Evolution of the volumetric water content (θ), Figure 3 – Daily rainfall (bars) and water flow during the studied average of four repetitions (full line) at 0.9 m of period (full line). Positive numbers indicate gain and depth, and soil water storage (H) until 0.9 m depth negative numbers indicate loss of water in the system. during the months of monitoring. –1 16 dose of fertilizer N was used (63 kg ha de N– (NH ) SO ) and crop N use efficiency (60%) was higher 14 4 2 4 NSSDS than the 10 to 40% recovery usually registered in other

) 12 experiments (Chapman et al., 1994; Trivelin et al., 1995; –1 NSSDF 10 Vallis et al., 1996). Using containers of 220 L, with the root system confined to an unrepresentative volume, 8 Trivelin et al. (2002) and Oliveira et al. (2002) showed 6 that the total amount of leached N was 4.5 kg ha–1 (none 4 of which was from the urea fertilizer), 53% of which occurred in the first three weeks due to poor develop- 2 Concentration (mg L (mg Concentration ment of the sugarcane root system and higher rainfall 0 in that period. 12/28 1/12 1/27 2/11 2/26 3/13 3/28 4/12 4/27 Although the observed leaching losses were low, Date other studies using tensiometers and soil solution ex- Figure 2 – Concentration of nitrogen in the soil solution derived tractors with porous cups between 0.8 and 1.20 m soil from soil (NSSDS) and N derived from fertilizer depths, with doses higher than 100 kg ha–1 of N, have (NSSDF) during the months of monitoring. registered leaching losses between 15 and 21 kg ha–1 in a Typic Hapludox cultivated with corn (Fernandes et there was an increase of the water flux at the 0.9 m depth al., 2006), 15 kg ha–1 in an Oxic Paleudalf cultivated with (Table 4). In the other periods, internal drainage was bean (Meirelles et al., 1980) and a maximum of 76 kg lower because θ was smaller than 0.236 m3 m–3 (Figure ha–1 of N in a Typic Hapludox in the second ratoon of 1), which corresponded to a K of 0.5 mm d–1 (equation sugarcane (Oliveira et al., 2001). In all cases mentioned 3). On average, 91 mm were drained during all cycles, the water drained was greater than 200 mm, in contrast which was 290 mm less than the surplus of 381 mm cal- with this work (91 mm). All these studies were per- culated by the climatological water balance method of formed in the State of São Paulo (Brazil) with similar Thornthwaite and Mather (1955), as described by climatological water balances to that of the Sentelhas et al. (2008). The capillary rise throughout the Pirassununga, showing that leaching losses could be cycle was very low, about 1 mm (Brito et al., 2009). higher if the conditions are favorable. Leaching N losses occurred mainly during periods The N concentration at 0.9 m depth was lower than 3 and 5 (Table 4), when the drainage was higher (Figure 10 mg L–1, the maximum limit for human consumption, 3). The total amount of N loss was 1.1 kg ha–1, of which in contrast to the findings of Oliveira et al. (2001), who – – + 37% was as N-NO3 , 11% as N-NO2 and 52% as N-NH4 . detected water quality alteration with an increase of From the analysis of the 15N isotope in the soil solution, the mean soil solution concentration at 0.9 m depth only 54 g ha–1 of nitrogen from the applied fertilizer (120 from 0.74 to 14.58 mg L–1 when 0 and 120 kg ha–1 of fer- kg ha–1) was leached during the crop plant cycle. tilizer N was applied to sugarcane. The concentration The amount of leached N, both native and derived of N in the soil solution at 0.9 m depth was one of the from fertilizer, was low, as observed in other studies causes of low loss by leaching. with sugarcane (Ng Kee Kwong and Deville, 1984; Individual events of high precipitation (Figure 3), Southwick et al., 1995). In field studies, Oliveira et al. when the soil profile was close to field capacity (Fig- (2000) did not find substantial amounts of N leached at ure 1), caused the higher values of drainage in the cycle 1.0 m depth in a Rodic Kandiudalf. In this case, a smaller (around 19 mm d–1). In consequence, N could easily be

Sci. Agric. (Piracicaba, Braz.), v.68, n.1, p.86-93, January/February 2011 Nitrogen fertilizer leaching in an Oxisol 91 lost since N was available in the soil, especially con- model APSIM-SWIM to show that of the 29.5 kg ha–1 of sidering the predominance of negative charges in the N-NO3 transported by drainage, the plants absorbed soil with low capacity of nitrate adsorption (see ΔpH 26.6 kg ha–1 of N from the soil below the depth of 1.5 in Table 1). Ghiberto et al. (2009) applied 120 kg ha–1 as m at the end of the cycle. It was concluded that the net labeled 15N urea to a sandy-clay-loam Arenic amount of N lost by leaching into the water table was –1 Kandiustults cultivated with sugarcane in a crop plant 2.9 kg ha N-NO3. cycle, and measured leaching losses at 0.9 m using ten- The N uptake by the crop was mainly native; how- siometers and soil solution extractors with porous cups. ever, the low fertilizer-N recovery (21%) by the whole Ghiberto et al. (2009) found that 18 kg ha–1 of N were plant (Franco et al., 2008) was not caused by higher N leached, mainly as nitrate, and that only 25 g ha–1 was leaching losses. Since volatilization was prevented at derived from the fertilizer. The of both experiments planting by incorporation of urea (Chapman et al., 1994; have similar textural class, hydraulic properties and Franco et al., 2008; Trivelin et al., 2002), we hypoth- millable stalk production; the main difference was the esize that the fertilizer N was immobilized in the soil amount and distribution of rainfall during the period in organic pool at the same time that soil organic N was which the surplus, calculated by the climatological wa- mineralized (Jansson and Persson, 1982). Furthermore, ter balance, normally takes place (December-March). In the high C/N ratio (80-120) of the residue results in an this study, compared to the experiment of Ghiberto et initial immobilization of soil mineral N and provision al. (2009), 115 mm less was drained and the month of of little N available for crop uptake in the year after January was drier than normal, as mentioned in the re- deposition (Thorburn et al., 2005), reinforcing the idea. sults. This is especially important in sugarcane systems with- –1 The production of millable stalks was 141 t ha (26% out straw burning where immobilization takes place of dry matter). The amount of N uptake by the crop (167 (Basanta et al., 2003; Meier et al., 2006; Wood, 1991), –1 kg ha ) was greater than the amount applied by fertili- and supports the conclusion of interference in biologi- –1 zation (120 kg ha ). So, the high demand of N may re- cal N immobilization having an effect on the downward strict the leaching of N. The crop N uptake was distrib- movement of fertilizer N (Ng Kee Kwong and Deville, uted as follows: 46% in stalks, 15% in dry leaves, 22% in 1987). There are few studies about leaching in this con- shoots, 7% in roots and 10% in rhizomes. The N recov- dition and in 2007 in the State of São Paulo, 40% of the –1 ered from the fertilizer by the crop was 25.4 kg ha in harvest took place without burning (Goldemberg et al., the whole plant, representing 21% of the applied fertil- 2008). In other studies, despite the low N leaching izer (Franco et al., 2008). In this experiment, at the end losses, significant amounts of K, Ca and Mg should of the crop cycle, sugarcane residue was not burnt be- have leached, which may result in soil acidification –1 fore harvest and it is estimated that 90 kg ha of N re- (Cahn et al., 1993; Ghiberto et al., 2009; Ng Kee Kwong mained in the field; this could be used in the subsequent and Deville, 1984; Oliveira et al., 2002). This is impor- first ratoon. tant if we consider that acidification is reversible by Leaching increases markedly when the nitrogen ap- liming, but when it takes place in the , amelio- plication rate is higher than that recommended for the ration is much more difficult and expensive crop (Thorburn et al., 2003). However, the soil N bal- (Hartemink, 2008). ance was negative when ignoring N input to the system arising from rainfall and biological fixation. In Brazil, Conclusion the recommended N doses in sugarcane crops are not as high as those used in other countries such as Austra- During the agricultural cycle of the crop plant, the lia (150-250 kg ha–1) (Gourley and Ridley, 2005; Stewart leaching of N was not considerable, mainly because the et al., 2006). Thus, it appears that an increase in crop N surplus of water between the months of December and use efficiency is beneficial, not only from the environ- March was lower than expected; the high demand of N mental point of view, but also due to the reduction of by the crop; and the analyzed cropping system did not costs by reduced use of nitrogen fertilizer (Chapman et include straw burning before planting. al., 1994). In periods in which the water flow and leaching Acknowledgements were greater, sugarcane was at the phenological stage of maximum growth with high demand for water and To the financial support by FAPESP and CAPES, to nutrients, thus contributing to avoid excessive loss of the logistical support of the São Luiz Mill, and to the N. Based on data of Franco et al. (2008) estimated that support of the laboratory analyses by the technicians at for periods 3 and 5 (Table 4), the sugarcane accumu- the Laboratory of Stable Isotopes at CENA. lated 5,047 and 4,461 kg ha–1 of dry matter, respectively. References According to Brito et al. (2009), the average actual –1 evapotranspiration was 11 and 8 mm d , respectively, Ball-Coelho, B.; Sampaio, E.V.S.B.; Tiessen, H.; Stewart, J.W.B. showing that the demand for N and water was high. 1992. Root dynamics in plant and ratoon crops of sugar cane. Similarly, Stewart et al. (2006) used the simulation Plant and Soil 142: 297-305.

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